The invention relates to a procedure for freezing a product that is to be subjected to the process of freeze-drying whereby the product is frozen and freeze-dried in a freeze-drying apparatus containing a freeze-drying chamber with shelves for performing the freeze-drying and a condenser with an evacuation pipe connection (for evacuating the freeze-drying chamber), the cooling surfaces of which are formed by a spiral tube in a number of tube coil layers, and where the coldness potential of the condenser is used to freeze the product. This invention also relates to a freeze-drying apparatus appropriate for carrying out said freeze-drying procedure.
Freeze-drying equipment of the type indicated here are known from the U.S. Pat. Nos. 3,077,036 and 4,035,924. The freeze-drying chambers are shown to have shelves where the product is placed during the drying process. For achieving the required vacuum and to precipitate the water vapor created during the drying process, condensers with pipe connections are provided which are located either inside the freezing chamber itself or in a separate chamber which is connected to the freezing chamber by piping and a closure valve. The cold surfaces of the condenser are commonly formed of spiral tubes in a circular tube coil array.
In the case of another freeze-drying apparatus of this type, the idea of using the coldness potential of the condenser to freeze the product that is to be freeze-dried has already been applied. In this case, the freeze-drying chamber is removably positioned on top of the condensation chamber. The axis of the spiral tube forming the cold surfaces of the condenser is vertically arranged. The process for freezing the product is provides that, initially, the freeze-drying chamber is removed from the condensation chamber. This way, the space of the spiral tube coil is accessible from the top. The container with the product to be freeze-dried is positioned in this space. A shortcoming is that there is no contact between the container and the spiral tube and that, therefore, the freezing process takes a relatively long time. Furthermore, the freezing procedure is rather complicated and can only be applied to relatively small product volumes. As a first step, the freeze-drying chamber has to be removed in order to place the product into the freezing chamber. Then the freeze-drying chamber is mounted only to be removed again after completion of the freezing process in order to be able to remove the frozen product. Finally, the freeze-drying chamber has to be mounted again in order to be able to perform the actual freeze-drying process.